1. Field of the Invention
The present invention relates to a liquid crystal display device and a manufacturing method for a liquid crystal display device, and more specifically to a transverse-field type of liquid crystal display in which display abnormalities caused by static electricity and the like are prevented.
2. Background of the Invention
A method of driving a liquid crystal display device that controls the liquid crystal by means of a transverse field is indicated, for example, in the Japanese Unexamined Patent Publication (KOKAI) No. 6-160878. Because a feature of a liquid crystal display of this type is that an electrical field is applied in a direction that is parallel to the surface of the liquid crystal cell, the change in the transmissivity of the liquid crystal cell that occurs when the liquid crystal molecules within the liquid crystal cell surface are twisted being used to make a display, in a liquid crystal display device that includes this liquid crystal cell, it is possible to obtain a clear view of an image, even when viewed at a large viewing angle, thereby enabling the achievement of a viewed displayed which is almost independent of the viewing angle.
However, along with a large viewing angle, there is a tendency for the liquid crystal cell to accumulate static electricity externally applied, thereby becoming electrically charged. This is described in detail below.
In the case of a transverse field type of a liquid crystal cell, because the liquid crystal is control by only an electrical field that is applied between a source electrode and a common electrode that are provided in a comb-like pattern on a TFT substrate, there is no electrode such as an ITO (indium tin oxide) electrode on the opposing color filter substrate film.
Therefore, if the surface of the polarizer on the color filter side is touched with the hand, the static electricity of the hand is picked up and passed via the color filter polarizer to the color filter glass substrate, resulting in a potential difference developing between the TFT substrate and the color filter substrate. The liquid crystal molecules, in response to this potential difference, exhibit faulty behavior and charging occurs.
In the past, a method of solving this charging problem, as shown in FIG. 4, was that of using a polarizer which was made by forming an ITO film 26 on the surface of the color filter polarizer, for example, as noted in the Japanese Unexamined Patent Publication (KOKAI) No. 4-51220. With this method, however, there are drawbacks, these being (1) a great increase in cost caused by the use of the sputtering method, (2) the occurrence of a loss of the ITO film because of the concentrated discharge current during ESD (electric static damage) testing, because of the excessively low resistance value of the ITO (sheet resistance is approximately 500 .OMEGA./.quadrature.), and (3) a tendency for the color of reflected light from the ITO polarizer to change, because of a change in the ITO film thickness and the resistance value thereof.
Another solution method, as shown in FIG. 5, was that of forming an ITO film 27 on the surface of the color filter, using sputtering. This method, however, has the drawbacks of (1) a great increase in cost caused by the use of the sputtering method, the same as the above-noted method of solution, and (2) difficulty in removing the adhesive glue that remains on the ITO film 27 when the polarizer is peeled away.
There is also the method, as in the Japanese Unexamined Patent Publications (KOKAI) No.6-313807, No.9-90391, and No.9-105918, of imparting electrical conductivity the adhesive material of the polarizer. With this method, however, all that is done is to make the adhesive electrically conductive, and there is no discription with regard to the resistance value, so that there remained the problem of not being able to prevent the loss of the electrically conductive layer when performing ESD testing.
Accordingly, an object of the present invention is to provide a novel liquid crystal display device which is an improvement over the above-noted drawbacks of the prior art, and which in particular not only prevents abnormal displays caused by static electricity, but also is not damaged by a discharge current occurring during an ESD test, and to provide a method of manufacturing the above-noted liquid crystal display device.
Another object of the present invention is to provide a liquid crystal display device which does not tend to exhibit a change in visually apparent color of externally applied light, and a method of manufacturing the above-noted liquid crystal display device.
Yet another object of the present invention is to provide a liquid crystal display device that enables easy exchanging of a polarizer and that is low in cost, and a method of manufacturing the above-noted liquid crystal display device.